As techniques for coating a variety of metal compound thin films on the surface of various types of substrates, a sputtering method, gas phase methods such as a vacuum deposition method, a sol-gel method, solution methods by thermal decomposition etc., of an organic acid metal salt or an organic metal complex have been known.
First, the sputtering method enables a compact and homogenous metal compound thin film to be formed on the surface of a substrate, and has been predominantly employed for the present. However, in the case in which the surface of the substrate has a complicated shape, it is impossible to form a metal oxide thin film on recessed portions.
Next, the gas phase methods are procedures that require high costs since it is necessary to prepare a thin film under a high-vacuum atmosphere. In addition, there is a problem of difficulty in obtaining a metal compound thin film having high crystallinity. Further, similarly to the sputtering method, to form a metal oxide thin film on recessed portions is impossible when the surface of the substrate has a complicated shape.
Subsequently, the sol-gel method requires time-consuming hydrolysis and polycondensation steps of the source material such as a metal alkoxide, in addition, there is a problem of not capable of readily applying when gelated due to difficulty in controlling the gelation reaction.
Finally, the solution method in which an organic acid metal salt or an organic metal complex is thermally decomposed enables a metal oxide thin film to be formed under an ordinary pressure even on the surface having a complicated shape. This method is a comparatively simple method since a thin film can be formed by merely carrying out thermal decomposition in the air under an ordinary pressure after an organic acid metal salt or an organic metal complex to be a precursor is dissolved in an organic solvent, and the solution is applied on the substrate with spin coating or the like. However, as in the sputtering method, formation of a compact and homogenous metal oxide thin film is difficult, and there is a problem of applicability to only limited source materials such as acetic acid salts, alkoxides and the like.